100 Years of General Relativity

Many people have been celebrating the centenary of the birth of Einstein’s Theory of General Relativity this year, but it’s not obvious precisely what date to select. I’ve decided to go for today, partly because the News on BBC Radio 3 did when I work up this morning, but also because there is a well-known publication that mentions that date:

The 25th November 1915 was the date on which Einstein presented the “final” form of his theory to the Prussian Academy of Sciences. You can find a full translation of the paper “The Field Equations of Gravitation” here. You will see that he refers to a couple of earlier papers in that work, but I think this one is the first presentation of the full theory. It fascinated me when I was looking at the history of GR for the textbook I was working on about 20 years ago that the main results (e.g. on cosmology, the bending of light and on the perihelion of mercury) are spread over a large number of rather short papers rather than all being in one big one. I guess that was the style of the times!

So there you are, General Relativity has been around for 100 years. At least according to one particular reference frame…

One of the main GR conferences (usually held every two years) is the Texas Symposium on Relativistic Astrophysics, so called because the first one was in Texas, organized by, among others, Wolfgang Rindler. This was 1963. Most television was black and white, the Beatles weren’t that big yet, and I wasn’t even born. The 50th anniversary symposium in 2013, again in Dallas, was, of course, among many other things (one of the attractions of the Texas Symposia in general is the large range of topics), retrospective with respect to its own history, but also with respect to 100 years of GR (depending on which date one picks). The next one is in December in Geneva (where I’m giving a talk) and of course to some extent is also influenced by 100 years of GR, though in general probably less retrospective than the one in 2013, though still special (geddit?!). The 50th Texas Symposium was also organized by Wolfgang Rindler, 89 at the time, who was in surprisingly good form (even driving Rocky Kolb to the venue for the public talk). Amazing to think that he was only about 10 years younger than I am now when he came to Dallas back in the day.

Even those who weren’t there can experience some of the talks and discusssions, as they have been put on YouTube. You can enjoy Engelbert Schücking’s (I remember reading his thesis in the library when I was in Hamburg) reminiscences (like Maarten Schmidt, he was too ill to travel, but sent a video which was shown at the conference), Rocky’s public talk, and a very interesting panel discussion involving a who’s who of GR, many of the leading players who are still alive. It’s really worth it to sit down and watch the whole thing. If you watch carefully, you can even see my balding head. 😐

Of personal interest to me were Ted Newman’s remarks. Additionally, he also gives a good impression of the joys of working in this field.

With regard to the STFC video, I really liked the last part. Initially, I was a bit let down when the narrator said that physicists will party if GR succeeded, but then was very happy when he said that they will also party otherwise.

Even if the video fails to make basic tenets of GR understandable to the lay public, I hope at least the last part makes up for it as a takeaway: that science, not just GR, is exciting regardless of which way the results go.

It is worth reminding ourselves that World War I had been under way for 16 months at that time, with Prussia dominating the other German States. The Western Front was firmly stalemated into trenches and there was more action on the eastern and southern fronts, while Gallipolli was being evacuated of Allied soldiers as a failure. The next year would see the slaughter at Verdun, to which even the Somme was intended as a diversion.

Phillip, I was at the same Texas meeting in Dallas.
I have a photo of 1993 Nobel laureate Joe Taylor tying the coat of Steve Weinberg after the latter’s talk. Given that Joe Taylor hardly gives talks, it was a rare occasion to see two great physicists in the same frame . Check out
In the picture you can also see Remo Ruffini, Nick Kaiser, Craig Hogan, Louis Witten, Cecile DeWitt etc

So, what progress since in the fundamentals of physics on the largest scales? Today I’d opt for gravity as a gauge theory governed by two gauge fields obeying first order differential equations (not the metric which obeys 2nd order ones). In the very transparent Cambridge formulation which expresses the theory using Clifford algebra the result predicts identically to GR in all tests run to date, but predicts differently where there is a nonzero fermion density.

Also, hare any generalisations of GR proved valuable? None that I am aware of, apart from the cosmological constant of which Einstein himself was (notoriously!) already aware.

[…] today, the 25th November, is the centenary of Einstein’s General Relativity – although as many physicists will point out, that statement depends upon your space-time reference frame (as we all saw in the film […]

Regarding history-of-GR books discussed above, I would like to add a large plug for “Einstein’s Jury: the race to test relativity” by Jeffrey Crelinsten. This tells the story of observational astronomy GR tests between about 1910-1930, and it makes it very clear that the famous Eddington 1919 eclipse result was not really decisive at the time; there was a much better eclipse measurement from Trumpler & Campbell in the mid-1920s, which is now largely forgotten. There’s also a lot about attempts to measure gravitational redshift from the Sun and Sirius B, which were controversial for a long time.

The book is superbly written, has fascinating detail on the personal battles e.g. East-vs-West coast animosities, and elderly traditionalists clinging to Newtonian ideas; it is well referenced and overall excellent. Probably requires undergraduate-level science background to get the most out of it, but not an advanced astronomy degree.